Browsing by Subject "Contact electrification"
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Item Open Access Charge dissipation mechanism of low-cost antistatic additive lignin in contact charged polymers(Bilkent University, 2019-07) Özel, MertcanContact electrification (C.E.), a phenomenon studied for millennia, develops contact charges on material surfaces, when two materials are contacted and then separated. Accumulation of contact charges and their uncontrolled sudden discharges on dielectric polymers pose major drawbacks in industries i.e. pharmaceutical, (micro)electronics, and space, causing million-dollar losses annually. The overall mechanism of C.E. is unclear until now, however, recent efforts have proven that chemical bond-breakages on polymer surfaces result in mechanoions – which are indeed the contact charges on the surfaces. These studies also showed that removing mechanoradicals (co-formed upon bond-breaking) by molecular radical scavengers destabilizes the mechanoions (charges) and render the doped polymer material antistatic. This method of static charge mitigation has an advantage over the conventional methods (e.g. doping with metals, carbon powder, conductive polymers, or surface humidity enhancers) because it is not based on an increase in surface conductance and smaller doping concentrations are needed to achieve antistatic behavior. However, currently used molecular radical scavenger doping is generally not cost effective method to be upscaled for industrial use. Lignin; however, is a “low-cost” material (the second most abundant polymer on earth, a by-product of paper production) that can act as a radical scavenger. In this thesis work, lignin was extracted from some examples of both hard and softwood. Firstly, it was verified that lignin doping in low concentrations (1 – 5% w/w) reduce the contact charge accumulation on common polymers such as on a crosslinked elastomer polydimethylsiloxane, and on thermoplastics polypropylene, polyethylene, polylactic acid, and polystyrene. Then, the mechanism of the observed charge dissipation was discussed in the light of the results obtained from surface conductance of polymers upon doping, 31P NMR and solid state 13C-NMR spectroscopy, total phenol content, and the reacted number of radicals before and after grinding - which was shown essential to get homogeneous doping- of lignin. The results pointed out a mechanism involving a radical scavenging activity without any change in the surface conductance of the material, similar to that with molecular radicals. The understanding of lignin’s charge dissipation mechanism will be helpful in industrial utilization of lignin as an antistatic additive and in assessment of the limitations of this utilization.Item Open Access Mechanism of triboelectricity: a novel perspective for studying contact electrification based on metal-polymer and polymer-polymer interactions(Bilkent University, 2016-08) Musa, Umar GishiwaThe static electricity that is generated when two identical or different materials come in contact with each other and separated is a well known physical phenomenon that has been studied for over 25 centuries. Contact charging occurs in technological and natural aspects of our everyday life. Generation of lightning and the feeling of unexpected shocks on dry days are excellent examples of naturally occurring phenomenon, while in technology it is used for photocopying and laser printing. Owing to the increase in energy consumption around the globe and demand for carbon emissions free energy sources, the triboelectric effect has recently being utilized as an e ffective means of harvesting mechanical energy and converting it into electricity for novel applications like powering portable electronic devices and self powered active sensing. Despite the fact that it has been known and applied for many years, the fundamental mechanism of contact electrification is still not fully understood. This study proposes a mechanism for triggering such triboelectric charge based on polymer-polymer and metal-polymer interactions. Conventionally, the mechanism of electrostatic charge generation is being presumed as a process giving rise to a combination of positive (arising from contact) and negative (arising from separation) charges in every single contact and separation. However, in our mechanism we propose a concept that shows combination of both positive and negative charges as \contact" and either positive or negative charge, depending on the initial contact-charge polarity of the material (due to surface charge mosaic), as \separation" charge. Different kinds of polymers like polydimethylsiloxane (PDMS), polytetra uoroethylene (PTFE), Polyethersulfone (PES) and polypropene (PP) were used in this study and similar characteristic was observed for all of the polymers. Thus, our perception of the working principle of triboelectri cation between two dielectric materials or a metal and a dielectric material is consistent and potentially vital in comprehending some unresolved controversies on triboelectricity.Item Open Access Online lubricant degradation monitoring using contact charging of polymers(Elsevier, 2022-05-15) Baytekin, Bilge; Baytekin, H. T.; Karluk, Azimet Akber; Ekim, Sunay DilaraLubrication of machine parts is necessary to prevent friction and wear in machine operation. However, oxidation of lubricants upon operation changes their chemical and physical properties and causes lubrication performance to deteriorate. Besides, one liter of wasted/used lubricant oil can contaminate a million liters of water. Current methods for the timely detection of oil deterioration lack practicality. Here we show simple, a triboelectrification-based method for oil degradation monitoring, in which the oxidation can be monitored by the changes in the contact charging (and separation) signals of oil-dipped cellulose and a common polymer tapped to each other. The commercial and base oil samples are oxidized at 100–200 °C for up to 80 h, simultaneously monitored by ATR-FTIR and the triboelectric method. The results show that a 40–90% decrease in the triboelectric open-circuit potentials in the presence of oxidized oil can directly indicate the start of oil oxidation without other accompanying analyses.Item Open Access Organic charge transfer cocrystals as additives for dissipation of contact charges on polymers(American Chemical Society, 2022-12-06) Ekim, Sunay Dilara; Kaya, Görkem Eylül; Daştemir, M.; Yildirim, E.; Baytekin, H. T.; Baytekin, BilgeCommon polymers can accumulate surface charges through contact, a phenomenon known since ancient times. This charge accumulation can have detrimental consequences in industry. It causes accidents and yields enormous economic losses. Many empirical methods have been developed to prevent the problems caused by charge accumulation. However, a general chemical approach is still missing in the literature since the charge accumulation and discharging mechanisms have not been completely clarified. The current practice to achieve charge mitigation is to increase materials conductivity by high doping of conductive additives. A recent study showed that using photoexcitation of some organic dyes, charge decay can be started remotely, and the minute amount of additive does not change the material's conductivity. Here, we show the contact charging and charge decay behavior of polydimethylsiloxane doped with a series of organic charge transfer cocrystals (CTC) of TCNQ acceptor and substituted pyrene donors (CTC-PDMS). The results show that the CTC-PDMS are antistatic, and the discharging propensity of the composites follows the calculated charge transfer degree of the complexes. On the other hand, the CTC-PDMS are still insulators, as shown by their high surface resistivities. Kelvin probe force microscopy images of the contact-charged and discharged samples show a quick potential decay in CTC domains upon illumination. Combined with the fast overall decay observed, the antistatic behavior in these insulators can be attributed to an electron transfer between the mechanoions in the polymer and the CTC frontier orbitals. We believe our results will help with the general understanding of the molecular mechanism of contact charging and discharging and help develop insulator antistatics.Item Open Access Preparation and characterization of polymer composites containing gold nanoparticles(Bilkent University, 2011) Yılmaz, EdaIn this study, light-assisted synthesis of gold nanoparticles in polymer films is demonstrated and characterization of gold nanoparticle-polymer composites using various techniques is shown. There are various methods introduced for the synthesis of gold nanoparticles in solution and their integration to the polymer films afterwards. However, synthesizing gold nanoparticles directly inside the polymer matrix is more advantageous for the production of polymer-nanoparticle composites. An advantage of synthesizing gold nanoparticles within polymer films is the opportunity of photo-patterning. Films having patterns made of regions with and without gold nanoparticles can be produced, using masks designed to cut off the radiation at desired places. Such patterned films were investigated with scanning electron microscope (SEM) and dark regions between irradiated regions and masked regions were observed. These dark regions are shown to be “ion depleted regions”, where gold ions diffuse through irradiated regions during the irradiation. These regions of about 10 m width, suggests a very large distance for gold ions to diffuse through a rigid matrix like Poly(methyl methacrylate)(PMMA), which is very interesting. Supporting evidence for the existence of these regions was obtained from fluorescence studies with Rhodamine 6G molecule and x-ray electron spectroscopy (XPS). The observations made through the formation of ion depleted regions can be used to estimate the diffusion constant of gold ions inside the PMMA matrix. Also the presence of ion depleted regions indicate the stability of photo-patterns created on the polymer film against smearing during light exposure after the production, by setting an upper limit to the critical feature size. During the characterization of gold nanoparticle-polymer composites, the electrical properties of PMMA with and without gold nanoparticles were investigated using charge resolved XPS, while applying external bias to the films with and without gold nanoparticles to probe the charging properties of the films. An enhancement of conductivity of PMMA films containing gold nanoparticles was observed using this technique. Additionally charge resolved XPS technique was also used to determine the charge storage characteristics of the polymer surfaces, which is important for the identification of charging mechanisms during contact and other electrification processes. It was shown that the PMMA surface is very susceptible to negative charging and even native negative charges on the PMMA surface can be observed prior to any treatment. Also when the surface is charged carbon and oxygen atoms of the carbonyl and methoxy groups of PMMA were observed to behave differently from the backbone of the polymer, which shows the chemical specificity of the charge accumulating spots on the surface.